1. Field of the Invention
The present invention relates to a liquid crystal display device. The invention particularly relates to a technique of securing a TFT substrate to a color filter substrate in which the TFT substrate has thin film transistors for pixels formed thereon and the color filter substrate is opposed to a glass substrate by way of liquid crystals.
2. Description of the Related Art
The liquid crystal display device has a structure of sandwiching liquid crystals between a first substrate and a second substrate. The first substrate has a plurality of drain lines and gate lines intersecting the drain lines formed thereon. The first substrate has pixels formed in regions surrounded by the drain lines and the gate linens. The first substrate has thin film transistors formed on every pixel. The second substrate has color filters of R (red), G (green), and B (blue) formed thereon, with the color filters forming pixels for color display. To secure the first substrate to the second substrate and seal the liquid crystals, the substrates are secured to each other by a sealing material, which is coated in a circular shape at the periphery of the second substrate. The liquid crystals are also sealed therewith. In the liquid crystal display device described above, alignment films for controlling the initial alignment of liquid crystal molecules are formed within the surfaces of the first substrate and the second substrate on the side of the liquid crystals in a region, where the liquid crystals are sealed and pixels are formed, that is, a so-called display area. To stably control the positioning accuracy of a coating device for the alignment films and the initial alignment of the liquid crystal molecules in the display area, the alignment films are generally coated as far as the region slightly exceeding the display area when the alignment films are formed.
In a liquid crystal display device mounted to a personal digital assistant including a mobile phone, it is demanded to enlarge the display area and increase fineness and image quality in a casing having a restricted size. For this purpose, the display area is enlarged by decreasing the ratio in which a frame region that does not contribute to image display occupies a space in the first substrate and the second substrate forming a liquid crystal display panel, that is, by narrowing a frame region (so-called narrow frame). This allows for multilayering interconnections in the frame region and improvement in fineness and image quality has been progressed.
However, in recent years, the distance from the end of the display area to the side edge of the liquid crystal display panel is about 1 to 2 mm, and worryingly the alignment film may overlap the coating region of the sealing material as the frame is further narrowed. In particular, since a polyimide-based material for forming the alignment film has a low adhesion, if the alignment film overlaps the coating region of the sealing material, adhesion among the sealing material, the first substrate, and the second substrate may be lowered.
The technique of improving the adhesion between the sealing material and the first and the second substrate includes techniques as described in JP-A-2001-66607 and JP-A-2008-46307. In the technique described in JP-A-2001-66607, a sealing material is coated such that the outer periphery of the sealing material coated at the corner of a liquid crystal display panel is at the outer side of the substrate than the outer periphery of the sealing material coated to the side. Further, the technique described in JP-A-2008-46307 is configured as follows. Over a region where the sealing material is coated from the side edge of the liquid crystal panel, an areas defined by removing part of a first insulation film is provided at four corners of the liquid crystal display panel and the sealing material is coated also to part of such areas to secure a pair of substrates.